We plan extended studies on synthetic analogs of the neurohypophysial hormones in which selected substitutions will be made to enhance specificity of actions and to enhance agonistic or antagonistic properties. We also plan studies on the kinetics of elimination of neurohypophysial peptides and the factors that influence rates of elimination. We will continue studies on the mechanisms by which neurohypophysial hormones influence renal hemodynamic and tubular functions in mammals, amphibians and fishes. BIBLIOGRAPHIC REFERENCES: Manning, M., J. Lowbridge, J. Haldar and W.H. Sawyer (1976a). Synthesis and some pharmacological properties of (1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine)oxytocin (hydroxy(4-Thr)oxytocin), a peptide with strikingly high oxytocic potency, and of (1-(L-2-hydroxy-3-mercaptopropanoic acid))oxytocin (Hydroxy-oxytocin). J. Med. Chem. 19:376-380. Sokol, H.W., E.A. Zimmerman, W.H. Sawyer and A.G. Robinson (1976). The hypothalamoneurohypophysial system of the rat: Localization and quantitation of neurophysin by light microscopic immunocytochemistry in normal rats and in Brattleboro rats deficient in vasopressin and a neurophysin. Endocrinology 98:1176-1188.